1. Field of the Invention
The invention relates to a semiconductor device for generating electromagnetic radiation, comprising a semiconductor body having successively at least a first semiconductor layer of a first conductivity type, a second electroluminescent semiconductor layer and a third semiconductor layer of the second opposite conductivity type, the first and the third semiconductor layers having a larger forbidden bandwidth than the second semiconductor layer.
2. Description of the Prior Art
Such a semiconductor device is known from French Pat. specification No. 2.287.109.
In order to increase the external efficiency and the light flux of such hetero structures, it is endeavored to improve the mechanism of the radiation combinations and this in particular by increasing the doping concentration in the material of the relative region.
It is to be noted that "electroluminescent material" is to be understood to mean herein a material in which the doping concentration is such that the internal quantum efficiency is approximately 80% and preferably more than 90%, in which the doping concentration is as high as possible to improve the radiation recombination, but on the other hand is sufficiently low not to adversely influence the crystal quality of the material.
In order to increase the external quantum efficiency it is also endeavoured to reduce the internal absorption, which is possible either by reducing the thickness of the radiative region if this has a direct band structure and strongly absorbs the emitted radiation, or by reducing the thickness of the other regions which are traversed by the emitted radiation. For example, the thickness of the substrate should be reduced locally when the structure consists of a substrate having several superimposed layers and the radiation emanates on the side of the substrate.
As described in said French Patent Application, the last-mentioned structure has been improved by causing a part of the emitted radiation to reflect on the side walls of the radiative region. However, the surfaces which are considered for this lateral reflection of the emitted radiation are comparatively small since the radiative region itself is very thin. In addition, on the one hand the local reductions in thickness of the substrate and on the other hand the shaping of the side walls of the radiative region to improve the reflection of the emitted radiation are delicate operations which are not very compatible with mass production.
It is one of the objects of the invention to avoid these disadvantages and to provide an electroluminescent device in the form of a hetero structure, the external quantum efficiency and the light flux of which are better than in the known device and the manufacture of which is compatible with mass production.